Integrated circuits (ICs) and other electronic devices often include arrangements of interconnected field effect transistors (FETs), also called metal-oxide-semiconductor field effect transistors (MOSFETs), or simply MOS transistors or devices. A typical MOS transistor includes a gate electrode as a control electrode and spaced apart source and drain electrodes. A control voltage applied to the gate electrode controls the flow of current through a controllable conductive channel between the source and drain electrodes.
Power transistor devices are designed to be tolerant of the high currents and voltages that are present in power applications such as motion control, air bag deployment, and automotive fuel injector drivers. One type of power MOS transistor device is a laterally diffused metal-oxide-semiconductor (LDMOS) transistor device. In an LDMOS device, a drift space is provided between the channel region and the drain region.
Power devices are susceptible to the generation of secondary charge carriers through impact ionization. In an n-channel LDMOS transistor device, electrons may generate additional electron-hole pairs after being accelerated in a region having a high electric field, such as near the drain boundary. If a sufficient number of holes—the secondary charge carriers—are created to raise the potential of the body of the LDMOS transistor device to an extent that the junction with the source is forward biased, activation of a parasitic npn bipolar transistor formed via the source (emitter), body (base), and drain (collector) regions of the LDMOS transistor device can occur. Very large, damaging currents can result via the activation of the parasitic bipolar transistor, an operating condition referred to as “snapback.”
LDMOS devices are often characterized by a “safe operating area” in which the operating current and voltage levels are below levels that would result in a snapback event. Attempts to remain within the safe operating area to avoid device destruction or other damage are often undesirably limiting factors for device operation and application.